I. Field of the Invention
The present invention relates to devices for preventing excessive voltage or current from damaging components in an electrical circuit, and more particularly, to fuses for domestic and especially automotive circuits.
II. Description of the Prior Art
Fuses are well-known devices for preventing excessive current from damaging electrical circuits and components in electrical circuits. In its simplest form a fuse consists of a piece of wire of controlled dimension and composition which is placed across a gap in a circuit. The fuse wire is intended to melt when the current through it reaches a predetermined value. The wire is chosen to suit the maximum current which the circuit and components can tolerate without damage. When the wire is subjected to such a current, the beat developed in it can no longer be dissipated quickly enough, and the wire melts. Once the wire has melted, current does not flow through the gap the wire once filled, and the circuit is effectively broken.
Several types of fuses and circuit breaking devices are known, but the use of each in relatively delicate but mass-produced circuitry (such as the type commonly employed in automobiles) has been subject to some drawbacks.
Simple rewireable fuses, that is, simple lengths of wire threaded between fuse terminals, are cumbersome because replacement after melting may be hampered by melted metal from the fuse wire which has adhered to the fuse terminals. Moreover, there exists the possibility of direct shorting, across the exposed terminals to which the fuse wire was connected, by some other wire or object.
Cartridge fuses comprise a hollow glass body containing a fuse wire, whose ends are connected to metal caps forming the fuse terminals. Although relatively inexpensive, such fuses are still more costly to manufacture and install than rewireable fuses. Moreover, the potential still exists for inadvertant shorting across the exposed fuse terminals or across the clips conventionally employed to connect these cartridge fuses to the circuit in which they are placed. Cartridge fuses of the type incorporating a plurality of narrow segments in the fusible elements, or which surround the element with a friable insulating powder, are of course more expensive to produce.
Electromechanical circuit breakers provide more certain breaking of the circuit, as do spring-biased, expulsion-type fuse links. Such devices, however, are even more expensive to manufacture than cartridge fuses, and take up more space when used. The limited space usually available and typically employed for installing fuses in locations such as in automobiles may not adequately accommodate the number of fuses necessary for the number of circuits present.